Yeasts as postfermentation agents in beer

Abstract

Saccharomyces cerevisiae and non-Saccharomyces yeasts are used since a long time in Belgian speciality beers for postfermentation improvements of maturating and conditioned beer. The use of S. cerevisiae strains is justified by carbonation effects and some oxygen removal. In contrast, the effects of non-Saccharomyces sp., which are present in sour beers mainly, are effective regarding flavour evolution predominantly. This study reviews successively the physiology (energy) aspects of the several yeasts species encountered in Belgian speciality beer and the potential of Saccharomyces cerevisiae strains by flavour modification after beer conditioning. The more practical aspects regarding pitching and yeast preparation are considered too. Further, several interesting features of Brettanomyces sp., Dekkera sp., Kloeckera sp., Candida sp., Cryptococcus sp. and Torulopsis sp. are studied. The influence of some enzymatic activity as alcohol dehydrogenase, aldehyde dehydrogenase, β-glucosidase and alcohol oxidase under peculiar conditions can allow the development of some typical flavours. The use of herbs, spices or fruit together with these yeasts will accelerate, modify, improve and probably, some-times, alter the "final touch" of the beer. Scientific research and projects are going on to understand and control further the production of speciality beers.